Allieu Kondewa helped lead the pro-government Civil Defence Forces (CDF), a notorious paramilitary unit which recruited traditional hunters to fight rebels during the brutal 1991-2002 civil war in the west African state.

He was convicted in 2007 of war crimes and crimes against humanity, including murder, issuing collective punishment and recruiting child soldiers.

He spent nearly 10 years in prison in Rwanda under a special agreement as war-ravaged Sierra Leone did not have proper detention facilities.

He returned to Sierra Leone on Sunday to serve out the last five years of his sentence, the court said in a statement.

"Kondewa... will be allowed to serve the remainder of his sentence in his community in Bo, subject to strict conditions and monitoring," the Residual Special Court for Sierra Leone said, referring to a main town in the south.

He has been ordered to acknowledge his guilt, publicly apologise and show remorse, the statement said.

Kondewa must report to the Sierra Leone police twice a month and cannot get involved in politics or "engage in secret meetings intended to plan civil unrest," it added.

The conflict, financed largely by so-called blood diamonds, left 120,000 people dead and tens of thousands mutilated.

As a parallel force to the regular army, the CDF fought rebels of the Revolutionary United Front (RUF) and the Armed Forces Revolutionary Council.

The CDF was alleged to have "eliminated" civilians suspected of collaborating with rebels, either through shooting them, hacking them to death or burning them alive.

Many locals however believe the CDF and its Kamajor fighters helped to rein in the brutal RUF rebels and protect villagers in the vulnerable hinterland of the diamond-rich country.

The Special Court for Sierra Leone, based in The Hague, and its successor were established by the UN in 2002 to try those who bore "the greatest responsibility" for the atrocities committed during the civil war.

"Convicts of crimes against humanity during the Sierra Leone civil war should be seen serving their sentence completely to deter others," rights campaigner Ibrahim Tommy told AFP in Freetown.

Fellow CDF commander Moinina Fofana was released in May after serving a 15-year prison sentence.

He was the first to complete a term imposed for war crimes by the UN-backed Special Residual Court for Sierra Leone.

Six war criminals are still in prison, serving sentences from 25 to 52 years.